BIO 303 Lecture Notes - Lecture 25: Lac Operon, Repressor, Tryptophan
10 May 2019
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Document Summary
All 3 structures transcribed, result in polycistronic mrna (bac) 1 mrna translated into 3 diff gene prod. Cistron: part of nucleotide sequence coding for single gene. Constitutive mutations: lacl and laco genes produce enzymes despite the presence or absence of lactose. Produces repressor: regulates transcription, gene regulation is lost. Lac promoter cannot bind to lac operator. Lac operon model: negative control: transcription occurs only when repressor fails to bind operator region. Repressor is allosteric; causes change in shape and chemical activity. Repressor normally binds dna sequence in operator region. Summary: no lactose: enzymes are not needed, genes encoding enzymes are repressed. Lactose present: indirectly induces activation of genes by binding repressor. All lactose metabolized: none available to bind to repressor transcription repressed. Three predictions from the operon model led to its validity. O region is involved in regulation no product. O region must be adjacent to structural genes to regulate transcription.
